The invention pertains to a ring oscillator comprising a closed chain of at least two modules.
The invention also pertains to a detector.
The invention further pertains to a receiver.
The invention further pertains to a device for reproducing an information carrier.
Ring oscillators are widely used. Such oscillators comprise a closed chain of at least two modules having an open loop gain of 1 and a total phase shift of 360xc2x0. In many applications it is desirable that the frequency at which the ring oscillator operates is controllable.
It is a purpose of the invention to provide a means for controlling the frequency of the ring oscillator. According to the invention at least one of the modules comprises a primary and a secondary amplifier stage and combination means for combining output signals of the primary and the secondary amplifier stage so as to generate an output signal of the module, the amplifier stages having a mutually different delay, the primary and the secondary amplifier stage each being coupled to an input of the module, the ring oscillator further comprising a control t for generating a first and a second auxiliary control signal for controlling the amplification of the primary amplifier stage and the secondary amplifier stage in response to an input control signal representative for the desired frequency for the ring oscillator.
In the ring oscillator of the invention the frequency can be easily controlled, by means of the control unit. In response to the input control signal the control unit generates a first and a second auxiliary control signal which control the amplification of the primary and the secondary amplifier stage. As the amplifier stages have a different delay this also causes a difference in the oscillation frequency of the ring oscillator. If for example the secondary amplifier stage has a higher delay an increase of the amplification of the secondary amplifier stage in combination with a decrease of the amplification of the primary amplifier stage will result in a lower oscillation frequency.
Although in principle it is sufficient if only one of the modules is arranged with such a parallel circuit according to the invention, the best controllability is obtained if eah of the modules comprises such a parallel circuit. Prefereably the modules are identical. In that case they may each be controlled by the same control unit.
With a ring oscillator according to the invention comprising two modules the frequency can be tuned within a ratio                     f        max                    f        min              ≈          5      /      3        ,
wherein fmax, and fmin resp. are the maximum and the minimum attainable frequency. If the ring oscillator according to the invention comprises three stages this ratio amounts about 2.
The ratio can be further increased by adding additional modules. This is however not necessary as the frequency range can be easily further extended by means of dividers.
Claim 2 describes a practical embodiment. The delay means may be implemented in various ways, for example by a RC network. The RC network need not comprise a separate capacitor, but may use parasitic capacitances of the active elements of the amplifier instead.